Field of the Invention
The present invention relates to the field of direct bonding, more specifically hybrid direct bonding, preferably at room or low temperature, and more particularly to the bonding of semiconductor materials, devices, or circuits to be utilized in stacked semiconductor device and integrated circuit fabrication and even more particularly to the fabrication of value-added parts in consumer and business products including image sensors in mobile phones, RF front ends in cell phones, 3D memory in high performance graphics products, and 3D memory in servers.
Description of the Related Art
Die, chip, or wafer stacking has become an industry standard practice to the continuing demands of increased functionality in a smaller form factor at lower cost. In general, stacking can be done with electrical interconnections between layers in the stack formed either as part of the stacking process or after the stacking process. An example of electrical interconnections formed after the stacking process is the use of through silicon via (TSV) etching and filling through one layer in the stack and into an adjacent layer in the stack to make electrical interconnections between layers in the stack. Examples of these three dimensional (3D) electrical interconnections formed as part of the stacking process include solder bumps and copper pillar, either with or without underfill, hybrid bonding and direct hybrid bonding. Realization of the 3D electrical interconnections as part of the stacking process is advantageous for a number of reasons including but not limited to eliminating the cost and exclusion requirements of TSV (through silicon via) technology. Direct hybrid bonding, also referred to as Direct Bond Interconnect (DBI®), is advantageous over other forms of stacking for a number of reasons including but not limited to a planar bond over metal and dielectric surface components that provides high strength at low temperature and enables 3D interconnect pitch scaling to submicron dimensions.
The metal and dielectric surface components used for a direct hybrid bond can be comprised of a variety of combinations of metals and dielectrics in a variety of patterns formed with a variety of fabrication techniques. Non-limiting examples of metals include copper, nickel, tungsten, and aluminum. See for example; P. Enquist, “High Density Direct Bond Interconnect (DBI™) Technology for Three Dimensional Integrated Circuit Applications”, Mater. Res. Soc. Symp. Proc. Vol. 970, 2007, p. 13-24; P. Gueguen, et. al., “3D Vertical Interconnects by Copper Direct Bonding,” Mater. Res. Soc. Symp. Proc. Vol. 1112, 2009, p. 81; P. Enquist, “Scalability and Low Cost of Ownership Advantages of Direct Bond Interconnect (DBI®) as Drivers for Volume Commercialization of 3-D Integration Architectures and Applications”, Mater, Res. Soc. Symp. Proc. Vol. 1112, 2009, p. 81; Di Cioccio, et. al., “Vertical metal interconnect thanks to tungsten direct bonding”, 2010 Proceedings 60th ECTC, 1359-1363; H. Lin, et. al., “Direct Al—Al contact using lot temperature wafer bonding for integrating MEMS and CMOS devices,” Microelectronics Engineering, 85, (2008), 1059-1061. Non-limiting examples of dielectrics include silicon oxide, silicon nitride, silicon oxynitride, and silicon carbon nitride. See for example P. Enquist, “3D Technology Platform—Advanced Direct Bond Technology”, C. S. Tan, K.-N. Chen, and S. J. Koester (Editors), “3D Integration for VLSI Systems,” Pan Stanford, ISBN 978-981-4303-81-1, 2011 and J. A. Ruan, S. K. Ajmera, C. Jin, A. J. Reddy, T. S. Kim, “Semiconductor device having improved adhesion and reduced blistering between etch stop layer and dielectric layer”, U.S. Pat. No. 7,732,324, B2 Non-limiting examples of a variety of patterns include arrays of vias or arrays of metal lines and spaces, for example as found in via and routing layers in CMOS back-end-of-line (BEOL) interconnect fabrication. Within these examples, 3D electrical interconnections may be formed by alignment and bonding of metal vias to metal vias, metal vias to metal lines, or metal lines to metal lines. Non-limiting examples of fabrication techniques to build a surface suitable for a hybrid bond are industry standard single and dual damascene processes adjusted to satisfy a suitable topography specification, if necessary.
There are basically two types of CMOS BEOL fabrication processes. One is typically referred to as an aluminum (Al) BEOL and the other is referred to as a copper (Cu) BEOL. In an Al BEOL process, Al with a suitable conductive barrier layer is typically used as the routing layer and tungsten (W), with a suitable conductive barrier layer is used for a via layer to electrically interconnect between two adjacent Al routing layers. The Al routing layer is typically dry etched and subsequently planarized with a dielectric deposition followed by chemo-mechanical polishing (CMP). The W via layer is typically formed with a single damascene process comprised of dielectric deposition, via patterning and etching to the previous routing layer, via filling with conductive barrier layer physical vapor deposition and W chemical vapor deposition, and CMP of W and conductive barrier layer to isolate W vias, or plugs, within the dielectric matrix. In a Cu BEOL process, Cu with a suitable conductive barrier layer is typically used as the routing and via layer. The Cu routing and via layers are typically formed with a dual damascene process comprised of dielectric deposition, via patterning and etching partially through the dielectric layer, followed by routing patterning that overlaps the via patterning and simultaneous continued etching of the via(s) to the previous routing layer where the routing overlaps the partially etched vias and etching of a trench for routing that connects to the previous routing layer with the via. An alternate dual damascene process is comprised of dielectric deposition, routing patterning and etching partially through the dielectric layer that stops short of the previous routing layer, via patterning and etching to the previous routing layer where the via is within the partially etched routing and the etching completes the via etch to the previous routing layer. Either doubly etched surface is then filled with a conductive barrier layer, for example by physical vapor deposition, followed by Cu filling, for example by electroplating or physical vapor deposition and electroplating, and finally CMP of the Cu and conductive barrier layer to isolate Cu routing within the dielectric matrix.
Use of either the industry standard W and Cu damascene process flows described above can be used to form a surface for hybrid bonding, subject to a suitable surface topography, for example as provided above. However, when these surfaces are used for hybrid bonding, there will typically be a heterogeneous bond component between metal on one surface and dielectric on the other surface, for example due to misalignment of via surfaces. This can result in via fill material from one bond surface in direct contact with dielectric from the other bond surface and without an intervening conductive barrier that is elsewhere between the Cu or W filled via and the surrounding dielectric.
It is preferable to have a wide process window with a low thermal budget for a direct hybrid bond process technology leveraging materials and processes that are currently qualified in a CMOS BEOL foundry to lower the adoption barrier for qualifying a direct hybrid bond process in that foundry. A Cu BEOL process is an example of such a preferable capability due to the Cu damascene process which has been an industry standard for a number of years and the capability of Cu direct hybrid bond technology to leverage this infrastructure. It has been relatively more challenging to leverage an Al BEOL industry standard process because the two primary metals in this process, W and Al, are more challenging materials to develop either a W or Al direct hybrid bond technology due to a combination of factors including high yield strength, coefficient of thermal expansion (CTE), native oxide, and hillock formation.